ASTM E679-04(2011)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E679 − 04 (Reapproved 2011)
Standard Practice for
Determination of Odor and Taste Thresholds By a Forced-
Choice Ascending Concentration Series Method of Limits
This standard is issued under the fixed designation E679; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The obtaining of odor and taste thresholds requires the sensory responses of a selected group of
individualscalledpanelists.Thesethresholdsmaybedeterminedinordertonotetheeffectofvarious
added substances on the odor and taste of a medium. They may also be determined in order to
characterize and compare the odor or taste sensitivity of individuals or groups.
It is recognized that precise threshold values for a given substance do not exist in the same sense
that values of vapor pressure exist. The ability to detect a substance by odor or taste is influenced by
physiological factors and criteria used in producing a response by the panelist. The parameters of
sample presentation introduce further variations.Thus, the flowrate of a gaseous, odorous sample has
an influence on the detectability of an odor. However, a concentration range exists below which the
odorortasteofasubstancewillnotbedetectableunderanypracticalcircumstances,andabovewhich
individuals with a normal sense of smell or taste would readily detect the presence of the substance.
Thethresholddeterminedbythispracticeisnottheconventionalgroupthreshold(thestimuluslevel
detectable with a probability of 0.5 by 50% of the population) as obtained by Practice E1432, but
rather a best estimate not far therefrom. The bias of the estimate depends on the concentration scale
steps chosen and on the degree to which each panelist’s threshold is centered within the range of
concentrationsheorshereceives.Theuseralsoneedstokeepinmindtheverylargedegreeofrandom
errorassociatedwithestimatingtheprobabilityofdetectionfromonly50to1003-AFCpresentations.
1. Scope 1.4 The medium may be a gas, such as air, a liquid, such as
waterorsomebeverage,orasolidformofmatter.Themedium
1.1 This practice describes a rapid test for determining
may be odorless or tasteless, or may exhibit a characteristic
sensory thresholds of any substance in any medium.
odor or taste per se.
1.2 Itprescribesanoveralldesignofsamplepreparationand
1.5 This practice describes the use of a multiple forced-
a procedure for calculating the results.
choice sample presentation method in an ascending concentra-
1.3 The threshold may be characterized as being either (a) tion series, similar to the method of limits.
only detection (awareness) that a very small amount of added
1.6 Physical methods of sample presentation for threshold
substance is present but not necessarily recognizable, or (b)
determinationarenotapartofthispractice,andwilldependon
recognition of the nature of the added substance.
thephysicalstate,size,shape,availability,andotherproperties
of the samples.
1.7 It is recognized that the degree of training received by a
This practice is under the jurisdiction of ASTM Committee E18 on Sensory
panel with a particular substance may have a profound influ-
Evaluation and is the direct responsibility of Subcommittee E18.04 on Fundamen- 2
ence on the threshold obtained with that substance (1).
tals of Sensory.
Current edition approved Aug. 1, 2011. Published August 2011. Originally
approved in 1979. Last previous edition approved in 2004 as E679–04. DOI: Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
10.1520/E0679-04R11. this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E679 − 04 (2011)
1.8 Thresholdsdeterminedbyusingonephysicalmethodof 3.1.9 ascending scale of concentrations—a series of in-
presentation are not necessarily equivalent to values obtained creasing concentrations of an odorous or sapid substance in a
by another method. chosen medium.
3.1.10 scale steps—discrete concentration levels of a sub-
2. Referenced Documents
stanceinamedium,withconcentrationsincreasedbythesame
2.1 ASTM Standards:
factor per step throughout the scale.
D1292Test Method for Odor in Water
3.1.11 3-alternative forced choice (3-AFC) presentation—a
E544Practices for Referencing Suprathreshold Odor Inten-
set consisting of one test sample and two blank samples (as
sity
applied to this practice).
E1432Practice for Defining and Calculating Individual and
3.1.12 geometric mean—the n th root of the product of
Group SensoryThresholds from Forced-Choice Data Sets
terms. In this method, the terms are concentration values.
of Intermediate Size
2.2 CEN Standards:
4. Summary of Practice
EN13725AirQuality—DeterminationofOdourConcentra-
tion Using Dynamic Dilution Olfactometry 4.1 A series of test samples is prepared by dispersing the
2.3 ISO Standards:
substance whose threshold is to be determined in the medium
ISO 13301 Sensory Analysis—Methodology—General ofinterest.Thisconcentrationscaleshouldincreaseingeomet-
Guidance for Measuring Odour, Flavour andTaste Detec-
ric increments so that any two adjacent concentration steps are
tion Thresholds by a Three Alternative Forced Choice separated by a constant factor.At each concentration step, two
(3–AFC) Procedure
blank samples consisting of the medium only are made
available to the panelist. The blank and test samples are
3. Terminology
encoded so that there is no visual, audible, tactile, or thermal
3.1 Definitions: differencebetweenthesamplesotherthancodedesignators (2).
3.1.1 sample—a material in any form that may or may not
4.2 The panelist starts at the lowest concentration step,
exhibit an odor or taste, depending on the amount of odorous
which should be two or three concentration steps below the
or sapid components that it may contain.
estimated threshold. Each sample within the set of three is
3.1.2 medium—any material used to dissolve, disperse, or
compared with the other two.
sorb odorous or sapid material whose threshold is to be
4.3 The panelist indicates which of the three samples is
measured.
differentfromtheothertwo.Achoicemustbemade,evenifno
3.1.3 blank sample—a quantity of the medium containing
difference is noted, so that all data can be utilized.
no added odorous or sapid material.
4.4 Individual best-estimate values of threshold are derived
3.1.4 test sample—themediumtowhichanodorousorsapid
from the pattern of correct/incorrect responses produced sepa-
material has been added at a known concentration.
rately by each panelist. Group thresholds are derived by
geometrical averaging of the individual best-estimate thresh-
3.1.5 detection threshold—the lowest concentration of a
substanceinamediumrelatingtothelowestphysicalintensity olds.
at which a stimulus is detected as determined by the best-
5. Significance and Use
estimate criterion.
3.1.6 recognition threshold—the lowest concentration of a
5.1 Sensorythresholdsareusedtodeterminethepotentialof
substanceinamediumrelatingtothelowestphysicalintensity substancesatlowconcentrationstoimpartodor,taste,skinfeel,
at which a stimulus is recognized as determined by the
etc. to some form of matter.
best-estimate criterion.
5.2 Thresholdsareused,forexample,insettinglimitsforair
3.1.7 best-estimate criterion—an interpolated concentration
pollution, in noise abatement, in water treatment, and in food
value, but not necessarily the concentration value that was
systems.
actually presented. In this practice it is the geometric mean of
5.3 Thresholds are used to characterize and compare the
the last missed concentration and the next (adjacent) higher
sensitivity of individual or groups to given stimuli, for
concentration.
example, in medicine, in ethnic studies, and in the study of
3.1.8 panelists—individuals whose odor or taste thresholds
animal species.
are being evaluated, or who are utilized to determine the odor
or taste threshold of the substance of interest.
6. Preparation of Concentration Scale
6.1 The concentration levels of the test substance in a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
medium should begin well below the level at which the most
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
sensitive panelist is able to detect or recognize the added
Standardsvolume information,referto thestandard’sDocumentSummary page on
substance, and end at (or above) the concentration at which all
the ASTM website.
Available from British Standards Institution (BSI), 389 Chiswick High Rd., panelists give a correct response.
London W4 4AL, U.K., http://www.bsigroup.com.
6.2 The increase in concentration of the test substance per
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. scale step should be by a constant factor. It is desirable to
E679 − 04 (2011)
obtain a scale step factor that will allow the correct responses 7.3 The judgments are completed when the panelist either
of a group of nine panelists to distribute over three to four (1) completes the evaluation of all sets of the scale, or (2)
concentrationsteps(seeAppendixX1-AppendixX3).Thiswill reaches a set wherein the test sample is correctly identified,
allow more accuracy in determining the group threshold value then continues to choose correctly in higher concentration test
based on the geometric mean of the individual panelists. sample sets.
6.3 Good judgment is required by the person in charge in
8. Data Evaluation
order to determine the appropriate scale step range for a
8.1 The series of each panelist’s judgments may be ex-
particular substance. This might involve the preparation of an
pressed by writing a sequence containing (0) for an incorrect
approximate threshold concentration of the odorous or sapid
choice or (+) for a correct choice arranged in the order of
substance in the medium of choice. The concentration of the
judgmentsofascendingconcentrationsoftheaddedsubstance.
substance may be increased two to three times for odorants or
1.5 to 2.5 times for sapid substances depending on how the 8.2 If the concentration range has been correctly selected,
perceived intensity of odor or taste varies with the concentra-
all panelists should judge correctly within the range of con-
tion of the substance providing the sensory response. For centration steps provided. Thus, the representation of the
example, if x represents an approximate odor threshold
panelists’ judgments as in 8.1 should terminate with two or
concentration, then a series of concentration steps would
more consecutive plusses (+).
appear as follows if a step factor of “3” were used:
8.3 Becausethereisafiniteprobabilitythatacorrectanswer
… x/27, x/9, x/3, x,3x,9x,27x.
will occur by chance alone, it is important that a panelist
continues to take the test until there is no doubt by that person
6.4 In actual practice, the various concentrations are ob-
of the correctness of the choice.
tained by starting at the highest concentration and diluting
three times per step, thus providing a series of dilution factors,
8.4 The best-estimate threshold concentration for the pan-
“V” being the initial volume:
elist is then the geometric mean of that concentration at which
i
the last miss (0) occurred and the next higher concentration
...729V , 243V,81V,27V,9V,3V , V,...
i i i i i i i
designated by a (+).
6.5 At each selected concentration or dilution, a 3-AFC
8.5 The panel threshold is the geometric mean of the
sample set consisting of one test and two blank samples is
best-estimate thresholds of the individual panelists. If a more
presented to panelists in indistinguishable fashion (3).Itis
accurate threshold value of an individual panelist is desired, it
desirable to have all samples prepared and ready for judging
may be obtained by calculating the geometric mean of the
before the evaluation session begins. (Reference (2) contains
best-estimate threshold of all series administered to that
sound practices for coding the samples, rotating the positions
person.
of these test and blank samples as the test proceeds, etc.)
6.6 If the samples are arranged in a left-center-right, or an
9. Report
above-center-below order, care must be taken that the test
9.1 Successful completion of the foregoing procedure pro-
sample is presented in one third of the presentations in the left
vides either the detection or recognition threshold of the
(top) position, one third in the center position, and one third in
substance in the medium of interest in accordance with this
the right (bottom) position to eliminate positional bias.
practice.
6.7 If only one sample at a time is available, the test and
9.2 The threshold value is in concentration or dilution units
blank samples may be presented one after another in units of
appropriate for the substance tested (4).
three presentations, with the test sample being randomized to
9.3 Forenhancedunderstandingofthethresholdresults,the
be the first, the second, and the third, and requesting the
following information is recommended:
response after all three samples in the set have been presented.
Better results, however, are obtained if the test and the two
Threshold of:
Procedure: ASTM Practice E679 (Rapid Method)
blanksamplesareavailableforadirectcomparison,sothatthe
Presentation:
panelist may sniff or taste back and forth at ease until a
Number of scale steps:
decision is reached.
Dilution factor per step:
Temperature of samples:
Panelist selection:
7. Judgment Procedure
Number of times test given:
Type of threshold (detection or recognition):
7.1 Thepanelistbeginsjudgingwiththatsetwhichcontains
Best-estimate threshold:
thetestsamplewiththelowestconcentration(highestdilution)
Individual:
of the odorous or sapid substance, takes the time needed to
Panel:
make a selection, and proceeds systematically toward the
9.4 RefertoAppendixX1-AppendixX3forexamplesofthe
higher concentrations.
calculations and reporting requirements.
7.2 Withineachset,thepanelistindicatesthatsamplewhich
10. Precision and Bias
is different from the two others (detection threshold) or which
exhibits a recognizable odor or taste of the substance (recog- 10.1 Because sensory threshold values are functions of
nition threshold). If the panelist cannot readily discriminate, a sample presentation variables and of individual sensitivities,
guess must be made so that all data may be utilized. interlaboratory tests cannot be interpreted statistically in the
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